Distributed process control systems, like those used in chemical, petroleum, or other processes, typically include one or more process controllers and input/output (I/O) devices communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses, or via a wireless communication link or network.
The field devices, which may be, for example, valves, valve positioners, switches, and transmitters (e.g., including temperature, pressure, level, and flow rate sensors), are located within the process environment and generally perform physical or process control functions, such as opening or closing valves, or measuring process parameters to control one or more processes executing within the process plant or system. Smart field devices, such as field devices conforming to the well-known Fieldbus protocol, may also perform control calculations, alarming functions, and other control functions commonly implemented within a process controller.
The process controllers (sometimes simply referred to as “controllers”), which are also typically located within the plant environment, receive signals indicative of process measurements made by field devices and/or other information pertaining to the field devices and execute a controller application that runs, for example, different control modules that make process control decisions, generate control signals based on the received information, and coordinate with the control modules or blocks being performed in the field devices, such as HART®, Wireless HART®, and FOUNDATION® Fieldbus field devices. The control modules in the process controller send the control signals over the communication lines or links to the field devices to control the operation of at least a portion of the process plant or system.
The particular arrangement of field devices, process controllers, control modules, and various other hardware and software elements utilized to control a particular process output may be referred to as a “control loop.” For example, a control loop for controlling a water level in a tank may include: (i) a level transmitter in a tank configured to measure the tank's water level; (ii) a process controller coupled to the level transmitter (e.g., via an I/O device) and configured to receive a level measurement obtained by the level transmitter; and (iii) a water inlet valve coupled to the process controller and configured to open or close based on control signals received from the process controller. A control loop may further include control modules (stored and/or executed by process controllers and/or field devices) configured to generate control signals based on an internal logic and one or more received measurements. For example, the control loop for controlling the water level may include control modules, stored and executed at the process controller, for generating control signals to open or close the water inlet valve based on the level measurements received from the level transmitter. A process plant may include hundreds or thousands of control loops for controlling various process outputs (e.g., tank levels, flow rates, temperatures, pressures, etc.).
Various plant personnel, such as configuration engineers, operators, and technicians, may interact with a control loop in a process plant. Generally speaking, configuration engineers create the control modules that are downloaded to the process controllers in the control loops. Operators monitor various variables in control loops and may set or change settings affecting run-time operation of the control loop (e.g., by adjusting set-points). Technicians and maintenance personnel may service devices in the field (e.g., process controllers and field devices), which may require taking the devices off-line.
Unfortunately, plant personnel often struggle to evaluate the condition or status of a control loop because plant personnel often must go through multiple menus, screens, and parameter lists of multiple function blocks in the control loop, for example, to appreciate the overall condition of the control loop. Moreover, even if plant personnel can somehow get a complete picture of the overall condition or status of the control loop, he or she may not fully appreciate how interactions with control loop devices and parameters affect other devices and parameters in the control loop. This difficultly with evaluating how interactions with a particular element of a control loop will affect other elements of the control loop can be attributed, at least in part, to the fact that plant personnel often have an unclear or incomplete idea of the structure (both logical and physical) of the control loop, or may not immediately be able to recall the entire loop, particularly if the control loop is complex in nature.
For example, configuration engineers may not readily recall how a new control module will affect parameters and field devices in the control loop. As another example, operators may not appreciate how changing a set-point or ignoring an alarm will affect other parameters or field devices in the control loop. Further, an operator may struggle to evaluate the status of a control loop because the elements of the control loop may have errors or conditions that are difficult to identify, and may not have a clear idea of which devices and control modules are included in a given control loop.
As yet another example, technicians and maintenance personnel may not always be aware of the impact their activities with respect to one or more devices in a control loop have on other devices in the control loop or in related loops. Specifically, a technician may not understand how the measurement or control devices being adjusted, replaced, taken off-line, etc. may affect the rest of the process. To the extent that maintenance personnel currently rely on documentation (rather than memory) to understand this aspect of their work, the documentation is frequently out of date because such documents, typically in the form of engineering drawings, are static and not always updated when changes are made within the plant. Additionally, such documentation typically includes loop sheets (devices and I/O), generated by the vendor, but no system context (control and operator displays). Clients frequently re-configure portions of the system after the loop sheets are generated and/or after the system is initially configured.